In technologies that use bearings, current bearing materials are made of various types of bearing steels. Alternative ceramic materials, such as silicon nitride, are superior to steel in areas such as hardness, corrosion resistance, Young's Modulus, and thermal expansion; however, steel maintains greater fracture toughness as compared to silicon nitride. Fracture toughness allows a material to resist further crack propagation upon initial damage, a highly desirable trait in the application of roller bearings especially in the roller elements for which this material is targeted. Fracture toughness is dependent on both the material composition and the material microstructure. Significant investigation has been conducted on silicon nitride bearing components; however, manufacturing quality of silicon nitride components is inconsistent as components tend to fail randomly and catastrophically as a result of internal defects. A more robust system and processing technique is desirable for bearing components.
Cemented tungsten carbide, such as WC—Co, is well known for its mechanical properties of hardness, toughness and wear resistance, thereby making it a popular material of choice for use in such industrial applications as mining and drilling. Because of its desired properties, cemented tungsten carbide has been the dominant material used in cutting tools for machining, hard facing, wear inserts, and cutting inserts in rotary cone rock bits, and substrate bodies for drag bit shear cutters. The mechanical properties associated with cemented tungsten carbide and other cermets, especially the unique combination of hardness toughness and wear resistance, make these materials more desirable than either metals or ceramics alone.
For conventional cemented tungsten carbide, fracture toughness is inversely proportional to hardness, and wear resistance is proportional to hardness. Although the fracture toughness of cemented tungsten carbide has been somewhat improved over the years, it is still a limiting factor in demanding industrial applications where cemented tungsten carbide inserts often exhibit gross brittle fracture that leads to catastrophic failure. Traditional metallurgical methods for enhancing fracture toughness, such as grain size refinement, cobalt content optimization, and strengthening agents, have been substantially exhausted with respect to conventional cemented tungsten carbide. The mechanical properties of commercial grade cemented tungsten carbide can be varied within a particular envelope by adjusting the cobalt metal content and grain sizes. For example, the Rockwell A hardness of cemented tungsten carbide can be varied from about 85 to 94, and the fracture toughness can be varied from about 8 to 19 ksi-sqrt (inch). Applications of cemented tungsten carbide are limited to this envelope. Additionally, traditional tungsten carbide lacks in its ability to acquire a smooth surface finish as a result of large particle size within a tungsten carbide compact.